Objects losing their transformations in scene when re-opening saved file
FBX files often come with default pose "animation". Make sure the objects don't have animation keyframes. You can tell if the location boxes in the properties-panel are yellow or green. Also if navigating between frames with left / right arrow keys causes them to reset.

As for workarounds you can make a new mesh object like a cube and navigate to "Mesh" tab and use the mesh dropdown to select the mesh of the imported object. That way you should have a clean, unmodified object using the imported mesh.